1. Field of the Invention
The present invention relates to a glass antenna amplifier, and more particularly to a compensating/amplifying device which utilizes a heating element incorporated in the glass of automobile windows as an antenna.
2. Prior Art
A device for using a heating element, which is incorporated in the automobile window glass for removing fog formed on the glass, as an antenna is disclosed in Japanese Laid-Open Patent Number 52-64,257. (which corresponds to U.S. Pat. No. 4,086,594 and U.K. Patent No. 1,520,030)
As illustrated in FIG. 5, in this prior art, a blocking circuit which includes a radio signal blocking coil 9 and a choke 7 for inhibiting interference is interposed between heating wires H and an automobile battery B. The radio signals, such as radio broadcasting signals, are picked up between the heating wires H and the blocking coil 9, and the picked-up signals are amplified by an auxiliary amplifier 13.
In the above prior art, the inductance of the blocking coil 9 is set at about 2 mH. Accordingly, high frequency signals received by the heating wires, which are used as an antenna, do not flow to ground but are sent to a radio receiver, etc. (not shown in the drawings) via the auxiliary amplifier 13.
The blocking coil 9 is wound on pot cores which have no air gaps. Also, since a direct current flowing through the heating wires H is about 10 A, relatively thick wire is required for the direct current to flow through the wires. Thus, the problem is that the size of the blocking coil 9 must be large enough to obtain the necessary inductance, and this results in an enlargement of the overall size of the compensating amplifier.
Further, in the above prior art, pot cores are used in order to render the overall size of the amplifier as small as possible. However, the pot cores are expensive, and a mirror-grinding must be done between the surfaces of the pot cores in order to eliminate the air gaps. This increases the manufacturing cost of the amplifier.